This invention relates generally to centrifugal chiller systems and, more particularly, to a method and apparatus for reclaiming oil from a cooler to the transmission of a centrifugal compressor.
In centrifugal compressors of the type which are used in large chiller type air conditioning systems, there is an inherent tendency for oil to migrate from the transmission to other parts of the system. In particular, during start-up and surge conditions, oil tends to migrate from the transmission into the motor, and hence to the evaporator or cooler. It was therefore necessary in such systems to provide the capability of reclaiming this lost oil and returning it to the transmission so as to allow continuous operation of the machine and to avoid degradation of the heat exchanger performance brought on by oil contamination.
The most common approach is to provide a stagnant cavity just downstream of the guide vanes in the compressor where oil may accumulate after being carried over with the main flow from the cooler. Some of the oil/refrigerant mixture may also be caused to flow directly from the cooler to the cavity because of the pressure difference between the two. An ejector, which is preferably driven by a source of gas from a compressor discharge, then functions to pump the oil from the cavity into the transmission of the compressor. This approach works fine for full load and part load operating conditions, but is unsatisfactory during operation in low load conditions. That is, when the guide vanes are closed down to accommodate low load operating conditions, the effectiveness of the ejector is substantially reduced. The reasons are twofold: first, the pressure at the compressor suction just downstream of the guide vanes is substantially reduced such that it is difficult to overcome the larger pressure difference between the low pressure cavity and the higher pressure transmission; and secondly, since the compressor discharge pressure is also reduced, the motive power of the ejector is substantially reduced. The result is that under low load operating conditions, the amount of oil that is pumped from the cavity into the transmission is substantially reduced, possibly to the point of inadequacy.
It is therefore an object of the present invention to provide an improved oil reclaim system.
Another object of the present invention is the provision for an oil reclaim system that functions properly at low load operating conditions.
Yet another object of the present invention is the provision for an oil reclaim system that operates irrespective of the load.
Still another object of the present invention is the provision for an oil reclaim system which is economical to manufacture and effective in use.
These objects and other features and advantages become more readily apparent upon reference to the following description when taken into conjunction with the appended drawings.